An operating system

If you already have Nextcloud running you can use the Nextcloud Forms app

Honestly, I would say because you just have less struggle. I had just a lot more problems when I was using Ubuntu instead of Debian. But I thinks it’s mostly personal preference

Maybe you could also try to generate your one SSL certificate and add it to your Android/Linux/Windows devices as root certificate 🤷🏼‍♂️.

That’s only a possibility, of you’re willing to do this to every single device that should be able to connect to your services